JPH11176446A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having superior charging and discharging cycle characteristics and output characteristic at high rate by forming a positive electrode mix of a positive electrode active material, a conductive auxiliary and a binder, and forming the conductive auxiliary of the fiber-like carbon material and the carbon material containing the granular carbon. SOLUTION: When the entire conductive auxiliary is set at 100 wt.%, a fiber-like carbon is preferably contained at 1-20 wt.%, and a granular carbon is preferably contained at 99-80 wt.%. The granular carbon contains the crystal carbon and the non-crystalline carbon, and in the case where the overall conductive auxiliary is set at 100 wt.%, the fiber-like carbon is preferably contained at 1-20 wt.%, and the granular carbon is preferably contained at 99-80 wt.% Furthermore, when the entire granular carbon is set at 100 wt.%, a crystal carbon is preferably contained at 90-60 wt.%, and a non-crystal carbon is preferably contained at 10-40 wt.%. It is preferable that the fiber-like carbon have an aspect ratio at 20-100,000 and a fiber diameter at 0.001-2 μm, and the granular carbon having an aspect ratio at 1-5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power source for a small portable electronic device, or a large industrial rechargeable battery for an automobile, a power storage, or the like.

[0002]

_2. Description of the Related Art Conventionally, transition metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ have been used as a cathode material for a Li secondary battery. It has significantly lower conductivity than metals or lithium alloyed metals. Therefore, graphite or an amorphous carbon material is mixed as a conductive aid to improve the conductivity in the electrode, mixed with a binder, and an electrode applied to a metal substrate is produced.

[0003] The carbon material serving as a conductive additive and the positive electrode active material are in contact with each other at a point or a plane. And the continuity is gradually lost. For this reason, the ability of the positive electrode active material cannot be fully utilized.

[0004] For example as a method of solving this problem, in JP-A -105459 discloses, using graphite LiMn ₂ O ₄ as a conductive additive in the total weight of LiMn ₂ O ₄ and graphite, the proportion of graphite from 8 2
It is disclosed that when the content is 2% by weight, the charge / discharge cycle characteristics are improved.

However, according to this method, even if the cycle characteristics are improved, the characteristics in the high-efficiency discharge are not sufficient unless more graphite is used, and if the amount of graphite increases, the active material filling density of the battery increases. However, it is not enough to realize a battery with high capacity and high output.

The reason is considered as follows. Because graphite creates a conductive path by contact between particles,
This is because the material itself does not have a conductive network and thus requires a large number of particles in order to obtain high current collection. In an electrode using graphite as a conductive agent, when high-efficiency discharge is performed, the amount of particles is small, so that the number of contact points with the active material is small, the current collecting property is insufficient, and the discharge capacity is reduced.

In order to improve cycle characteristics, dibutyl phthalate (DBP) oil absorption is 50 ml / 100 g to 3 g / ml.
The use of less than 00 ml / 100 g of carbon black is proposed in JP-A-7-296794. This is because by utilizing the large oil absorption, the electrolyte is immersed in the battery, and by utilizing the swelling of the electrodes, the inside of the battery is also used to eliminate insufficient pressure due to loose winding between the electrodes.
It is proposed that the charge / discharge cycle characteristics be improved.

However, when a carbon material or carbon black having a large oil absorption is actually used, the oil absorption is large, so that it is difficult to prepare a slurry at the time of electrode coating, and a large amount of a binder is absorbed. It is difficult to produce a positive electrode that maintains mechanical strength by maintaining bonds between particles.

Therefore, it is necessary to increase the binder,
As a result, there is a disadvantage that the packing density of the positive electrode active material is reduced.

[0010] Further, it is difficult to increase the electrode density due to the large bulk density of the carbon black, and the press pressure must be increased in order to increase the electrode density. If the height is increased, a problem arises in that the base material and the mixture are separated. For this reason, it was difficult to increase the volume energy density of the battery. Further, in a long cycle, the mechanical strength of the electrode is insufficient, so that the current collector and the mixture are separated, and there is a problem in cycle characteristics.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery which has improved conductivity in a positive electrode and electrode strength, and has excellent charge / discharge cycle characteristics and high-rate output characteristics. To provide.

[0012]

The present invention has been completed by employing the technical means described below in order to solve the above-mentioned problems.

The features of the lithium secondary battery according to the present invention are as follows.
In a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte and utilizing a lithium ion insertion / desorption reaction, a positive electrode mixture is composed of a positive electrode active material, a conductive auxiliary, and a binder. The agent is a carbon material, and is composed of a fibrous carbon material and granular carbon. When the entire conductive assistant is 100% by weight, the ratio of the fibrous carbon is 1 to 20% by weight,
The particulate carbon is composed of 99 to 80% by weight. The addition of the fibrous carbon makes it possible to alleviate the volume stress caused by the expansion and contraction of the electrode, thereby facilitating the maintenance of the structure. In addition, the addition of granular carbon increases the number of contact points with the active material, resulting in low resistance. By mixing the fibrous carbon with a smaller weight ratio than the granular carbon, it is possible to suppress a decrease in the conductivity of the electrode due to expansion and contraction.

Another feature of the lithium secondary battery according to the present invention is that, in a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, utilizing a lithium ion insertion / desorption reaction, the positive electrode mixture is The conductive aid is a carbon material, and includes a fibrous carbon material and granular carbon. The granular carbon includes crystalline carbon and amorphous carbon. And the proportion of the fibrous carbon is from 1 to 20.
% Of the granular carbon is 99 to 80% by weight, and the ratio of crystalline carbon to amorphous carbon in the granular carbon is 9% by weight of the granular carbon as 100% by weight.
0 to 60% by weight and 10 to 40% of the amorphous carbon.

Still another feature is that the fibrous carbon of the conductive additive of the positive electrode has a length aspect ratio (hereinafter, referred to as an aspect ratio) to a fiber diameter of 20 to 100,000, and a fiber diameter of 0.001. When the average particle size of the amorphous carbon is 1 when the ratio of the average particle size of the crystalline carbon to the average particle size of the amorphous carbon in the conductive additive of the positive electrode is High carbon is 0.004 or more and 0.05 or less.

Although fibrous carbon has a longer conductive path than graphite, it is difficult to efficiently contact the active material surface when the fiber diameter is about 5 μm or more, and electrons are not sufficiently supplied to the active material. High-efficiency discharge is difficult.

Therefore, in the present invention, it is preferable that the fiber diameter is small and the length is such that a sufficient conductive path can be formed in the electrode. The fibrous carbon forms a conductive path in the electrode, and the fiber diameter is 0.001-2 μm and the length is about 20 μm, and a material having a certain length can easily maintain the electrode. .

As the granular carbon mixed with the carbon fiber, crystalline carbon represented by graphite in the granular carbon is used. As a result, the electrode density increases, and the average particle size becomes 1
By mixing fine amorphous carbon black carbon having a size of not more than μm, shortage of contact points of crystalline carbon is compensated for, and the conductivity in the electrode is increased and the liquid collecting property is improved.

By mixing these, it is possible to increase the electrode density and to increase the active material filling amount. Therefore, a battery having a high volume energy density and excellent cycle characteristics and high rate discharge characteristics can be realized.

The present invention relates to a lithium secondary battery, wherein a conductive auxiliary for an electrode is added to fibrous carbon 1 to 20 with respect to the entire conductive auxiliary.
%, And 99 to 80% of the granular carbon, to produce an electrode. The battery has little problem of electrode peeling, has a long life, has a high volume energy density, and further has a 10 to 10% of the total granular carbon.
A battery using an electrode in which 40% is made of amorphous carbon and the remaining 90 to 60% is made of graphite-based carbon is based on the finding that it has higher performance.

[0021]

Embodiments of the present invention will be described below.

First, the features of the lithium secondary battery according to the present invention as a summary of the findings obtained by the present inventors will be described, and the outline of the embodiment will be described. Specific examples obtained as knowledge will be described later.

A lithium secondary battery according to the present invention for achieving the above object comprises a positive electrode, a negative electrode and an organic electrolytic solution. The conductive additive to be used is a mixture of fibrous carbon and granular crystalline carbon and / or amorphous carbon.

As the positive electrode active material, a transition metal oxide, a transition metal sulfide, a polyaniline-based organic compound, or any other active material can be used, but Li _x Ni _1-y M is particularly preferable. _y O ₂ , Li _x M _1-y Co _y O ₂ , Li
_{x Mn 1-y M y O} 2 (0 <x ≦ 1.3, 0 ≦ y ≦ 1,0 ≦ z
<2, M: Al, Fe, Cu, Co, Mg, Ca, V,
Ni, Ag, Sn, at least one of the second transition metal elements), a lithium-containing manganese oxide such as LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , or Li _x Mn _{2-y MyO.
4-z} (0 <x ≦ 1.3, 0 ≦ y <2, 0 ≦ z <2, M: A
1, Fe, Cu, Co, Mg, Ca, V, Ni, Ag,
Sn, at least one of the second transition metal elements).

On the other hand, as the negative electrode active material, metallic lithium, lithium alloy (for example, LiAl, LiPb, LiS
n, LiBi, LiCd, etc.), a conductive polymer doped with lithium ions (eg, polyacetylene, polypyrrole, etc.), and an interlayer compound (eg, TiS ₂ , MoS ₂ ) containing lithium ions mixed in the crystal. Or a carbonaceous material capable of doping or undoping lithium, an intermetallic compound such as silicide, a metal oxide, or any material capable of inserting and extracting lithium.

As the electrolytic solution, an aprotic organic electrolytic solution in which a lithium salt is used as an electrolyte and the electrolyte is dissolved in an organic solvent is used. Here, as the organic solvent, esters, ethers, 3-substituted-2-oxazolidinones, a mixed solvent of two or more of these, and the like are used. To be more specific, examples of the esters include alkylene carbonates (ethylene carbonate, propylene carbonate, γ-butyrolactone, 2-methyl-γ-butyrolactone) and the like, and chain dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like. It is.

As ethers, diethyl ether,
Dimethoxyethane, diethoxyethane, cyclic ether,
For example, the ether having a 5-membered ring is tetrahydrofuran and its substituted product, dioxolane, and the ether having a 6-membered ring is 1,4-dioxolane, pyran, dihydropyran, tetrahydropyran and the like. As the electrolyte, lithium perchlorate, lithium borofluoride, lithium aluminate, lithium halide, lithium trifluoromethanesulfonate, LiPF ₆ , LiAs
F ₆ and LiB (C ₆ H ₅ ) ₄ can be used, and among them, lithium phosphorus fluoride, lithium borofluoride and lithium perchlorate are preferable.

However, any organic electrolyte using a lithium salt as a supporting electrolyte can be used and is not limited to the above examples.

As a conductive assistant for the positive electrode, a fibrous carbon material and a granular carbon material are mixed, and the granular carbon material is mixed with graphite particles and an amorphous carbon material to form an active electrode. By making the ratio of the substance 90% by weight or more and reducing and optimizing the ratio of the weight of the binder and the weight of the conductive assistant, a battery with a high volume energy density, a high rate characteristic and a long life can be realized.

As described above, the disadvantage of the fibrous carbon material is that the number of contact points with the active material is small, and it is necessary to increase the amount of addition in the electrode alone. In addition, compared to graphite, because of its fibrous shape, it does not collapse like graphite, and it is difficult to increase the electrode density. In addition, since carbon fibers typified by vapor-phase synthetic carbon fibers and the like are expensive in synthesis cost as compared with other carbon materials, using them in large quantities increases the cost of the battery.

On the other hand, an advantage of the fibrous carbon material is that a conductive path is formed in the electrode, the volume stress against the expansion and contraction of the electrode can be reduced, and the structure can be easily maintained. In addition, there is an advantage that the specific surface area is small and slurry preparation is easy.

When a graphite material is used as a conductive additive for the positive electrode, if the average particle size is 5 μm or less and the specific surface area is 10 m ² / g or more, the resistance is reduced when a large current of about 2 C is applied. There is a problem that the capacitance characteristic is largely inferior.
However, the oil absorption is small and slurry preparation is easy.
Further, when the electrode is pressed, graphite is easily oriented, so that a high electrode density can be easily obtained, and a large amount of active material can be filled in the battery, which is effective for improving the energy density of the battery.

Carbon black-based ketjen black and acetylene black have a large oil absorption and are difficult to prepare slurries, and have a low bulk density, so that it is difficult to obtain a high mixture density. There is a problem that the mechanical adhesion with the substrate is weak. However, these have a well-developed structural structure with good electron conductivity,
Further, since the average particle size is as small as 0.1 μm or less, there are many contact points with the active material in the electrode, and the current collecting property is high, so that the rate characteristics are very good. Furthermore, the cycle characteristics are considered to be good because the electrolyte can be sufficiently captured in the electrode.

In the present invention, the configuration of the conductive assistant for the electrode is as follows. A carbon fiber having a fiber diameter of 0.001 to 2 μm and an aspect ratio of more than 200 is
By adding 20% by weight, it is easy to maintain the structure in the electrode, and 99 to 80% by weight of granular carbon having an average particle size of 5 μm or less
In addition, the contact point between the conductive additive and the positive electrode active material is increased by weight%. Further, in the granular carbon contained in the conductive additive, the particle size is 0.3.
The electrode density is increased by adding 5 to 5 μm of graphite to 60 to 90% by weight, and amorphous carbon such as carbon black ketjen black or acetylene black having a particle size of 80 nm or less is reduced to half or less of the whole granular carbon, preferably. 10-40
By adding wt%, the number of contact points with the active material was increased to form a conductive network, and an effectively high-performance electrode was realized.

The addition of the carbon fiber makes it possible to reduce the volume stress caused by the expansion and contraction of the electrode. In addition, the addition of carbon black increases the liquid-collecting properties,
Resistance drops. Here, the particle size of the carbon material of the carbon black based on amorphous carbon is 0.0 with respect to the particle size of graphite.
When the ratio is not less than 04 and not more than 0.05, it is possible to efficiently enter the positive electrode active material and the graphite, or between the graphite, the fibrous carbon material and the gap where they cannot be sufficiently contacted, and increase the contact points, An electrode having higher conductivity can be realized. By mixing these carbon materials and using them as a conductive additive, it becomes possible to obtain a high-density electrode and to increase the active material filling amount. for that reason,
A battery with a high volume energy density can be realized.

Further, by synthesizing the conductive additive in this way, the synergistic effect of improving the cycle characteristics, particularly the capacity characteristics when the discharge rate is increased, and realizing a long service life was realized.

The carbon fibers that can be used in the conductive additive of the present invention include vapor-phase synthetic carbon fibers having a fiber diameter of 1 to 20 μm,
Nanotubes, pitch-based fibers, PAN-based fibers, mesophase pitch-based fibers, etc., of up to 50 nm can be used, but gas-phase synthetic carbon fibers or nanotubes are preferred from the viewpoint of tensile strength and resistance. Among carbonaceous materials and graphite materials, graphite materials are more preferable because they have a lower resistance value, a higher density, and a greater effect of improving the electrode density.

The crystalline carbon used in the present invention is artificial graphite or natural graphite having an average particle diameter of 1 to 5 μm, mainly having an aspect ratio of the major axis to the minor axis of 1 or more and 5 or less.
The specific surface area by BET method is 10 m ² / g or more and 300 m ² or more.
/ G or less, and low in ash, L
Both c and La are preferably 240 ° or more.

The particle shape may be scaly, massive, or anisotropic. As the amorphous carbon material, there is no restriction on the type and production history of carbon black, and various types such as furnace black, channel black, thermal black, acetylene black, and Ketjen black can be applied. Preferably, those having a hollow shell structure such as Ketjen Black or acetylene black having a developed structure structure are preferable. Most desirably, it is performed in a system in which the electrode density increases.

The structure of the positive electrode of the present invention uses a mixture of carbon fiber, artificial graphite, and carbon black as a conductive additive, mixes it with a positive electrode active material that is a lithium-containing transition metal oxide, and forms a binder. The positive electrode was produced in the above. With this configuration, the contact area between the positive electrode active material and the conductive additive becomes larger than before, so that the resistance in the electrode decreases, and the overvoltage during charging and discharging decreases, thereby improving the capacity characteristics.

Further, when the granular carbon is simply mixed with the positive electrode active material as a conductive auxiliary as in the conventional case, the space between the positive electrode active material and the conductive auxiliary is caused by expansion and contraction of the grid of the positive electrode active material during charge and discharge. Although the peeling of the gradual progress, there was a problem that charging and discharging to the positive electrode active material is not performed smoothly, but when using the conductive auxiliary of the present invention, the positive electrode active material and fibrous carbon,
Since the contact between the positive electrode active material and the conductive additive is favorably maintained due to the coexistence of granular carbon, a battery with less deterioration of the positive electrode due to cycling can be realized.

With the electrode using the conductive auxiliary of the present invention,
Suppression of electrode collapse and improvement of electron conductivity are realized, and cycle characteristics and output characteristics can be improved.

Comparative Example 1 First, a comparative example will be described. The positive electrode was produced as follows. Artificial graphite (8.7% by weight) having an average particle size of 5 μm and lithium manganate (87% by weight) having an average particle size of about 20 μm as a positive electrode active material were used as a conductive additive.
Was mixed with PVDF (polyvinylidene fluoride) (4.3% by weight) as a binder dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) to form a paste.
It was applied to both sides of an Al foil having a thickness of 20 μm and dried at 80 ° C. for 3 hours. Thereafter, the resultant was molded under pressure at a pressure of about 2.0 ton / cm ² and heat-treated at 120 ° C. for 3 hours in a vacuum to obtain a positive electrode. The density of the mixture layer of this positive electrode was about 3.0 g / cm ³ .

The negative electrode was manufactured by the following method. PVDF solution is used as a binder for artificial graphite
The mixture was mixed so that VDF became 10% by weight, and NMP was added to form a paste. The paste was applied to both sides of a copper foil collector having a thickness of 23 μm, and dried at 80 ° C. for 3 hours. Thereafter, the mixture was roll-formed by a roll press until the mixture density reached about 1.57 g / cm ^3, and then dried in a vacuum at 120 ° C. for 2 hours.

The positive electrode, the negative electrode, and a polyethylene porous membrane separator having a thickness of 25 μm were combined and wound into a battery can having an outer dimension of 14 mm × 47 mm as shown in FIG. 1M-LiPF ₆ / EC ₊ DMC as an electrolyte
The characteristics were evaluated using (1: 1).

Similarly, as a second and a third comparative example, a positive electrode was prepared by using acetylene black as a conductive additive, and the electrode density was 2.4 g / cm ³ . When Ketjen Black was used as the conductive additive, if the conductive aid was 8.7% by weight and the binder was 4.3%, peeling occurred after drying after electrode coating, and electrode preparation was impossible. . For this reason, Ketjen Black was prepared with 6% by weight of the conductive additive and 7% by weight of the binder. Otherwise, the electrode was treated in the same manner, and the electrode density of the obtained electrode was 2.6 g / cm ³ .

The obtained positive electrode was manufactured under exactly the same conditions as in the case where graphite was used as the conductive additive, except for removing the positive electrode, and the characteristics were evaluated.

(Example 1) N-Methyl-2- (2-wt%) was added to a conductive additive (8.7 wt%) obtained by mixing various types of fibrous carbon and granular carbon and lithium manganate (87 wt%) as a positive electrode active material. A binder, PVDF (polyvinylidene fluoride) (4.3% by weight) dissolved in pyrrolidone (hereinafter abbreviated as NMP) was mixed and made into a paste, and then applied on both sides to a 20 μm-thick Al foil. Dried at 80 ° C. for 3 hours. After that, about 2 to
After pressure molding at a pressure of n / cm ² , heat treatment was performed in vacuum at 120 ° C. for 3 hours to obtain a positive electrode.

[0049]

[Table 1]

Table 1 shows the mixing ratio of carbon and the density of the mixture layer of these electrodes. Also, the battery capacity and the current density when a battery was prepared in the same manner as in Comparative Example 1 except for the positive electrode were 0.2C.
When a charge / discharge test was performed in a voltage range of 4.2 V to 3.5 V, the discharge capacity retention rate at 500 cycles (discharge capacity at n cycles / initial discharge capacity), the discharge rate was 3 CmA and the lower limit voltage was 3 Table 1 also shows the ratio of discharge capacity maintenance to 0.2 C (discharge capacity at 3 CmA / discharge capacity at 0.2 CmA) when discharging to 0.5 V together with Comparative Example. It can be seen that, by combining fibrous carbon and granular carbon with the conductive additive, the applicability at the time of producing the electrode is improved, and the performance of the battery is also improved as compared with the comparative example.

(Embodiment 2)

[0052]

[Table 2]

As a second embodiment, carbon black and acetylene black, which are amorphous carbon, and crystalline artificial graphite were mixed with granular carbon other than fibrous carbon as a conductive additive, and the respective ratios were changed. In Examples 2A to 2K, electrodes were produced in the same manner as in Example 1. In Example 2L, an electrode was manufactured under the same conditions as in Example 1 except that the positive electrode active material was mixed at a ratio of 90% by weight, the conductive additive was mixed at a ratio of 6.7%, and the binder was mixed at a ratio of 3.3% by weight. . These granular carbons had a shape having an aspect ratio in the range of 1.0 to 5.0. Fibrous carbon having a fiber diameter of 0.2 μm and an aspect ratio of 100 or more was mixed at a ratio of 20% by weight.

The mixing ratio of carbon and the density of the mixture layer of these electrodes, the battery capacity when a battery was prepared in the same manner as in Comparative Example 1 except for the positive electrode, and the current density were 0.2 V and 4.2 V ~ 3.5
The discharge capacity retention rate at 500 cycles (discharge capacity at n cycles / initial discharge capacity) when the charge / discharge test was performed in the voltage range of V, the discharge rate at 3 CmA, and the discharge rate at the lower limit voltage of 3.5 V Table 2 shows the 0.2C discharge capacity retention ratio (discharge capacity at 3 CmA / 0.2 CmA discharge capacity).

In these examples, both the coating properties and the adhesiveness were good, the discharge capacity retention rate was as high as 80% or more, and the discharge capacity was 80% or more in 3C discharge. Rate characteristics have been improved and improved. In particular, it was found that high performance was obtained when the ratio of amorphous carbon in granular carbon was 10% to 40%.

It was found that when a battery was manufactured using carbon black as the granular carbon and artificial graphite having an average particle size of 1 μm, a battery with improved rate characteristics, capacity density, and cycle characteristics was obtained.

(Embodiment 3) Next, an embodiment of a device using the lithium secondary battery according to the present invention will be described. As a built-in power supply for a portable personal computer, it has the same configuration as that of the battery described in Embodiment 2 and an outer dimension of 18 mm in diameter.
A cylindrical cell having a size of 65 mm was manufactured, and an assembled battery was manufactured using the cylindrical unit cell to obtain a battery pack. For comparison, a battery configuration similar to that shown in Comparative Example 1 was used, and the diameter was 18 mm ×
A 65 mm cylindrical single cell was prepared, and a battery pack was prepared.

The battery pack to which the present invention was applied had good rate characteristics, and the charging time could be reduced by 50% compared to Comparative Example 1. In addition, the capacity retention rate after 100 charge / discharge cycles showed a good property of 99% or more. As described above, it has been found that the portable personal computer incorporating the lithium secondary battery according to the present invention has a short charging standby time, and significantly improves the usability of the user. Also,
As a backup power supply, it can be used for a long time, thereby avoiding the possibility of memory loss.

In this embodiment, a portable personal computer has been described, but a radio, a compact disk player, a cassette recorder, a magneto-optical disk player, an MD player, and a portable device employing a lithium secondary battery according to the present invention as a power source. TV, mobile phone, pager, PHS, pocket computer,
Laptop personal computer, mobile terminal,
Portable devices such as electronic organizers, portable electric devices, shavers, etc., electronic devices used as backup power sources such as arithmetic devices and storage devices incorporating lithium secondary batteries, communication devices such as facsimile and cordless telephones, refrigerators and air conditioners Household electronic and electrical equipment such as conditioners, rechargeable vacuum cleaners, cordless irons, electric vehicles, motorcycles, motorized bicycle golf carts, electric wheelchairs,
It goes without saying that the performance of an electric assisted bicycle, an electric power storage device such as an outdoor emergency power source, etc. can be improved as compared with the conventional device, similarly to the present embodiment.

[0060]

As is apparent from the above description, according to the present invention, an electrode having an increased active material filling rate by increasing the strength of the electrode, the conductivity in the electrode and the mixture density of the electrode is improved. Creation is easy. As a result, a high-performance lithium secondary battery having a high volume energy density and a good discharge rate characteristic and further improved charge / discharge cycle characteristics can be realized.

Further, if the apparatus or system employs the lithium secondary battery according to the present invention, there is an effect that a lightweight, high-performance and stable operation is realized. And miniaturization of equipment and systems using the lithium secondary battery according to the present invention,
This has the effect of extending the life.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an exploded configuration of a cylindrical lithium secondary battery according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode terminal, 2 ... Separator, 3 ... Negative electrode, 4 ... Positive electrode,
5 ... Negative electrode terminal.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Ren Muranaka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (11)

[Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte and utilizing a lithium ion insertion / desorption reaction, wherein the positive electrode mixture comprises a positive electrode active material, a conductive auxiliary, and a binder. The conductive auxiliary agent is a carbon material, and includes a fibrous carbon material and granular carbon. 2. A lithium secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and utilizing a lithium ion insertion / desorption reaction, wherein the positive electrode mixture comprises a positive electrode active material, a conductive auxiliary, and a binder. The conductive additive is a carbon material, and includes a fibrous carbon material and granular carbon. When the total amount of the conductive additive is 100% by weight, the ratio of the fibrous carbon is 1 to 2%.
A lithium secondary battery comprising 0% by weight and 99 to 80% by weight of the granular carbon. 3. A lithium secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and utilizing a lithium ion insertion / desorption reaction, wherein the positive electrode mixture comprises a positive electrode active material, a conductive auxiliary, and a binder. Is, the conductive additive is a carbon material, including fibrous carbon and granular carbon, granular carbon, crystalline carbon,
It contains amorphous carbon, and when the whole of the conductive additive is 100% by weight, the ratio of the fibrous carbon is 1 to 20% by weight, and the granular carbon is 99 to 80% by weight. Lithium secondary battery. 4. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte and utilizing a lithium ion insertion / desorption reaction, wherein the positive electrode mixture comprises a positive electrode active material, a conductive auxiliary, and a binder. Is, the conductive additive is a carbon material, including fibrous carbon and granular carbon, granular carbon, crystalline carbon,
When amorphous carbon is contained and the entire conductive additive is 100% by weight, the ratio of the fibrous carbon is 1 to 20% by weight, the granular carbon is 99 to 80% by weight, and The ratio of crystalline carbon to amorphous carbon in the granular carbon is 90 to 60% by weight of the crystalline carbon and 10 to 40% of the amorphous carbon, with the granular carbon being 100% by weight. Characteristic lithium secondary battery. 5. The fibrous carbon according to claim 1, wherein the shape of the fibrous carbon contained in the conductive additive of the positive electrode has an aspect ratio of 2 or more.
0 or more and 100000 or less, and the fiber diameter is 0.001 or more and 2
Lithium secondary battery having a particle size of 1 μm or less and an aspect ratio of carbon particles of the granular carbon is 1 or more and 5 or less. 6. A method according to claim 3, wherein the ratio of the average particle size of the crystalline carbon to the average particle size of the amorphous carbon is such that the average particle size of the crystalline carbon is less than the average particle size of the crystalline carbon. The lithium secondary battery according to claim 1, wherein the ratio of amorphous carbon is 0.004 or more and 0.05 or less. 7. A lithium secondary battery according to claim 1, wherein the lithium secondary battery is a radio, a compact disk player, a cassette recorder, a magneto-optical disk player, an MD player, a portable television, a portable telephone, a pager. , PHS, a pocket computer, a laptop personal computer, a mobile terminal, an electronic organizer, a portable electric device, a shaver, and the like. 8. An electronic apparatus comprising a lithium secondary battery according to claim 1, wherein said electronic apparatus is used as a backup power supply for an arithmetic unit, a storage device, or the like. 9. A communication device, such as a facsimile or a cordless telephone, and a refrigerator, an air conditioner, a rechargeable vacuum cleaner, and a cordless iron using the lithium secondary battery according to claim 1 as a power supply. Home electronic and electrical equipment. 10. An electric vehicle, a motorcycle, a bicycle with a motor, a golf cart, and an electric wheelchair, wherein the lithium secondary battery according to any one of claims 1 to 6 is used as a power source for a running motor. ， Motor assisted bicycle. 11. An outdoor emergency power supply and a power storage device, wherein the lithium secondary battery according to any one of claims 1 to 6 is used as a battery for storing power.